This invention relates to a key lock, and more particularly, to a magnetic key lock provided with an alarm system. The key lock includes a normally closed first switch connected to the alarm system, and a normally open second switch associated with a tumbler of the lock, and also connected to the alarm system so that the alarm system is activated when the second switch is closed upon movement of the associated tumbler by a key or pick inserted into the key slot of the lock. Additionally, a magnetic sensor is provided adjacent the key slot so that a proper magnet-bearing key can activate the magnetic sensor before the second switch is closed by the tumbler movement in order to delay the activation of the second switch for a selected time period to allow the proper key to turn the lock cylinder in order to open the first switch, and, therefore, inactivate the alarm system.
In my U.S. Pat. No. 3,962,695, I disclosed a Magnetic Key Lock And Alarm, including a pair of switches located at the rear end of the key slot of the magnetic key lock. One of the switches is normally open and is closed by any key engaging the switch when the key is fully inserted into the key slot. The second switch is normally closed, and includes a mass of iron thereon to be directed by a magnet embedded in a proper key in order to open the second switch when the key is fully inserted in the key slot. The alarm and the first and second switches are connected in a series circuit to cause the alarm to sound when both the first and second switches are closed upon the insertion of a non-magnet bearing key in the key slot.
Due to the constant engagement and disengagement of the first switch of my above patent by the insertion of the key, it is possible that the first switch can be bent, or even broken by the key or a lock pick, thus inactivating the alarm. Furthermore, it is noted, that after continuous use, the second switch could become very flexible and contact the proper magnet-bearing key when inserted in the key slot, so that the magnet-bearing key, if fabricated from metal, would become part of the electrical circuit and cause the alarm to sound. Therefore, there is a need for an improved magnetic key lock which overcomes the above structural defects of my above-mentioned patent.